Flotation is a separation technique commonly used in the dressing of minerals and crude ores for separating valuable materials from the gangue. Non-sulfidic minerals and ores in the context of the present invention include, for example, calcite, apatite, fluorite, scheelite, baryta, iron oxides and other metal oxides, for example, the oxides of titanium and zirconium, and also certain silicates and aluminosilicates. In dressing processes based on flotation, the mineral or ore is normally first subjected to preliminary size-reduction, dry-ground, but preferably wet-ground and suspended in water. Collectors are then normally added, often in conjunction with frothers and, optionally, other auxiliary reagents such as regulators, depressors (deactivators) and/or activators, in order to facilitate separation of the valuable materials from the unwanted gangue constituents of the ore in the subsequent flotation process. These reagents are normally allowed to act on the finely ground ore for a certain time (conditioning) before air is blown into the suspension (flotation) to produce a froth at its surface. The collector hydrophobicizes the surface of the minerals so that they adhere to the gas bubbles formed during the activation step. The valuable constituents are selectively hydrophobicized so that the unwanted constituents of the mineral or ore do not adhere to the gas bubbles. The valuable material-containing froth is stripped off and further processed. The object of flotation is to recover the valuable material of the minerals or ores in as high a yield as possible while at the same time obtaining a high enrichment level of the valuable mineral.
Surfactants and, in particular, anionic, cationic and ampholytic surfactants are used as collectors in the flotation-based dressing of minerals and ores, in particular of calcite which is of considerable value especially for the paper industry. Calcite represents an important filler with the ability for adjusting the whiteness and transparency of the paper. Calcite minerals, however, are often accompanied by silicates so that, to purify the calcite, the silicate—which is undesirable for many applications—has to be removed. Another problem which has a serious impact on the selectivity of the froth flotation process is related to the magnesium content of the minerals or ores. Magnesium salts seriously improve the stability of the froth, which collapses slowly and therefore increases the flotation time, while the selectivity drops. In order to overcome the disadvantages known from the state of the art, for example, International patent application WO 97/026995 (Henkel) suggests the use of readily biodegradable mixtures of quaternised mono- and diesters of fatty acids and triethanolamine (so-called mono/diesterquats). Although said esterquat mixtures show a superior biodegradability when compared with other cationic collectors, the products still do not lead to satisfactory recovery of the valuable material, in particular calcite minerals, when used in economically reasonable quantities.
Accordingly, an object of the present invention is to provide improved collectors which make flotation processes more economical, i.e. with which it is possible to obtain either greater yields of valuable material for the same quantities of collector and for the same selectivity or at least the same yields of valuable materials for reduced quantities of collector. A second object is to supply collectors which simultaneously meet the needs for high biodegradability.